Data Communication Between Industrial Control Instrument And Monitoring Configuration Software

1. Introduction

At present, the intelligent instruments used in industrial field usually have the function of data communication. For the measurement and control equipment with fieldbus technology and standard communication interface, when they are configured by configuration software, because the configuration software is oriented to open measurement and control equipment, it is easy to establish the communication between industrial control PC and equipment. However, RS232 or RS485 communication mode is still widely used in industrial measurement and control instruments. Compared with fieldbus technology, RS232 and RS485 can only represent the physical medium layer and link layer of communication. If we want to realize two-way access to data, we must write our own communication application program. However, most of these programs can not meet the ISO / OSI specifications, and can only achieve a single function, which is suitable for a single type of device, and the program is not universal. In view of this situation, this paper introduces how to use OLE technology of windows, other third-party application development tools to generate ActiveX control for data communication, and real-time database interface ActiveX control provided by configuration software to realize data communication between instrument and industrial computer system.

2. Structure of industrial control configuration system

The industrial control configuration system is mainly composed of industrial field control instrument, detection instrument and industrial control computer. The system is configured by monitoring configuration software. The overall structure of the system is shown in Figure 1. The industrial field instrument realizes the field control, monitoring, display and real-time data transmission. The operation data of each control or detection point on the site is transmitted to the upper industrial control computer by RS-485 communication interface in real time. The industrial control computer calculates, analyzes, processes and stores the operation data of each point on the production site, and generates the real-time operation process curve of each point on the site, operation parameter data table, diagnosis and alarm of each fault condition, etc.

3. ActiveX control for data communication

The I / O device driver of industrial control configuration software is a bridge between configuration software and I / O devices such as PLC and intelligent instrument. It provides a good data communication environment for I / O devices with standard communication interface. But for the instrument with non-standard communication interface, it is difficult and inconvenient to develop by the manufacturer's special development software. However, the industrial control configuration software is usually a standard control container, which supports windows ActiveX Control Based on Component Object Model (COM) technology, which can be automatically called from outside. Therefore, we can use VB, VC + + or other third-party application development tools to generate data communication ActiveX controls for control instruments, and package them in the form of OCX. The configuration software registers and inserts the data communication activcx control through the control manager, directly refers to the properties and methods of the data communication AC ivex control in the built-in program language script program, and calls the special data communication function to send data to the field instrument or return the field data to the configuration software. So as to realize the data communication between configuration software and industrial field instrument.

4. Real time database interface control

Industrial control configuration software itself also provides many ActiveX controls, among which real-time database interface control device Dbcom is specially provided for external third-party programs. The real-time database db of configuration software is an open data platform. Dbcom has various standard interfaces. Users can use Dbcom to access the data in the database db of configuration software in various common development environments (such as VB, VC +, C ", etc.). Users can access real-time data, historical data and set data in DB through Dbcom. The data accessed can be a local database or a database on other remote computers on the network [1]. First, the data communication program between the industrial control computer and the on-the-spot instruments is compiled by VC+. Then the DBCOM control is invoked, and all variables that need to exchange data with the field instruments are defined by attribute Tag-Pars in the DB database. In the data communication program, once the communication with the field instrument is successful, the specific control method provided by Dbcom can be used to access the database in the configuration software to realize the data communication between the field instrument and the configuration software. Dbcom also has the function of event processing. When the data changes, the event on dataChanged will be automatically generated to notify the variable serial number or the variable name defined by the attribute tagpars, and refresh the changed data value. This will simplify the programming of data communication program and improve the real-time performance of data communication between field instruments and industrial control configuration software.

5. Concluding remarks

For the industrial field instruments whose data communication interface does not conform to the ISO / OIS specification, it is difficult to program their data communication through the I / O device driver of the configuration software when they are configured by the industrial control configuration software. This paper introduces a method of data communication between industrial field instrument and industrial control configuration software by using OLE technology and control programming. It is a simple and effective method in practical engineering application.

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